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है”ह”ह

IS 1985-1 (1980): Recommended practice for preparation ofiron and steel for electroplating, Part 1: high carbonsteel [MTD 24: Corrosion Protection]

IS:198!i(Part I)-1980

Indian Standard RECOMMENDED PRACTICE

FOR PREPARATION OF IRON AND STEEL FOR ELECTROPLATING

PART I HIGH CARBON STEEL

( First Revision )

Metallic Finishes Sectional Committee, SMDC 23

Chairman

Dxx S. KBI~EN_~~BTEY

Members

DRS.L.N. ACHARAYULU

Representing

Indian TeIephone Industries Ltd, Bangalore

SERI I. N. BHATIA ( Alter&e ) Ministry of Defcnce ( R&D )

ASSISTANT DIRE~T;~T~~EEM ) , Ministry of Railways RESEARCH, STANDARDS ORGANIZAT~~, LUCKNOW

CHEMIST & METALLURQIBT, INTEGRAL COACH FAOTORY, MADRAS ( Alternate )

SERI K. BALA~RISHNAN Central Electrochemical Research Institute

SERI S. R. NATABAJAN ( Alternate ) ( CSIR ), Karaikudi

SEEI M. Y. BORKER SHRI P. K. SEN ( Alternate )

Ministry of Defence ( DGI )

SHRI M. S. CHAKRAVORTY Premier Metal Finishers ( P ) Ltd, Calcutta Srmr AHINDRA CHATTERJEE Canning Mitra Phoenix Ltd, Bombay

SHRI S. V. KULKARNI ( Alternate ) SHRI D. K. CHATTERJEE Sen-Raleigh Ltd, Asansol SERI 0. P. CHHABIZA Bharat Heavy Electricals Ltd, Hardwar

SERI R. M. SIN~HAL ( Alternate ) SHSI KANTILAL T. DALAL Kohinoor Electra-Gilders, Bombay

SHRI JAYENDRA K. DALAL ( Alternate ) SERI P. K. DESWANDE The Premier Automobiles Ltd, Bombay

SERI A. G. PRABHU ( Aftmute ) SERI C. P. DEY Hindustan Motors Ltd, Calcutta SERI M. Z. KHAI~ Geep Flashlight Industrier Ltd, Allahabad

SHRI K. A. SIDDIQUI ( Alternate )

( Cimtinued on pags 2)

(0 C@yr&ht 1980

INDIAN STANDARDS INSTITUTION

This publication is protected under the Indian Copvright Act ( XIV of 1957 ) and reproduction in whole or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act.

IS : 1985 ( Part I ) - 1980

( Confinuedffom page 1 )

Members RCpCS&i?lg

SERI V. S. KULKARNI Grauer and Weil ( India) Ltd, Bombay SHRI SUSHIL GOINKA ( Alrernut~ )

SH~I S. PANOHAPAKEBAN T. I. Cycles of India, Madras SHRI R.VENKATARAY~(A~~~~~~U~~)

SKRI S. K. RAY National Metallurgical Laboratory ( CSIR ),

SHRI S. K. ROY Jamshedpur

Indian Posts & Telegraphs Department, Calcutta DEPUTY GENERAL MANAQER ( Alternate )

_ -

SKIU R. Sl<N Hindustan Cables Ltd, Rupnarainpur ( Dist Burdwan )

SHRI KALYAN GHOEH ( Alternatr) StiRI R. A. SHAH Ronuk Industries Ltd, Bombay

KUMARI MRIDULA A. SHAH ( Alternate ) DR R. C. SHARMA Eveready Flashlight Company, Lucknow SXRI V. THIOABAJ~ Development Commissioner, Small Industries

Services Institute, New Delhi SERI C. R. RAMA RAO,

Director ( Strut 8s Met ) Director General, IS1 ( Ex-o&cio Member)

Secretaries SHRI S. L. BALI

Deputy Director ( Met ), ISI

SERI 0. N. DAS~UPTA Deputy Director ( Met ), IS1

.

2

IS : 1985 ( Part I ) - 1989

Indian Standard RECOMMENDED PRACTICE

FOR PREPARATION OF IRON AND STEEL FOR ELECTROPLATING

PART I HIGH CARBON STEEL

( First Revision )

0. FOREWORD

0.1 This Indian Standard ( Part I) ( First Revision ) was adopted by the Indian Standards Institution on 10 June 1980, after the draft finalized by the Metallic Finishes Sectional Committee had been approved by the Structural and Metals Division Council.

0.2 Electroplating of plain high carbon steel introduces problems not found in similar operations relating to low carbon steel. During the cleaning and plating cycle, high carbon steel differs from low carbon steel because of its greater tendency to become embrittled and the greater difficultv in obtaining maximum adhesion of the electro-deposit. Prepara’tion of high carbon and low carbon steels was earlier covered in IS : 1985-1962*. While reviewing this standard, it was decided to cover the various steps involved in the preparation of these steels in three parts. Preparation of low carbon steel is covered in Part II; while preparation of iron castings is covered in Part III. Preparation of non- ferrous metals for electroplating will be covered in a separate standard.

1. SCOPE

1.1 This standard ( Part I ) is intended as an aid in establishing and maintaining the preparatory cycle for electroplating of high carbon steel producing a minimum hydrogen embrittlement and maximum adhesion of electro-deposited metal. For the purpose of electroplating there is no generally recognized demarcation between the high and low carbon steels but for the purposes of this standard, steels containing O-35 percent or more carbon are considered as high carbon steels.

*Code of practice for pretreatment of steel, copper and copper base alloys, zinc and zinc base alloys for electroplating.

IS : ‘1985 ( Part I) i 1980

1.2 This standard does not apply to plating of alloy steels.

2. PRELIMINARY PRETREATMENT PROCEDURE

2.1 Oil, grease, dirt drawing compounds, burnt-in metal, heavy scale, etc, are the contaminantswhich need to be removed for obtaining the required quality of plating. The following preparatory treatments are necessary for this purpose.

2.1.1 Precleaning - Solvent-degreasing with clean solvent, spray- washing or emulsion-cleaning, followed by electrolytic or soak-alkali cleaners, are recommended. The solvent degreasing is preferred to reduce the burden on the alkali treatments. Soak-alkali cleaning is usual for parts that are to be barrel plated. Electrolytic cleaning should always be anodic where the control of embrittlement is a problem.

2.1.2 Stress Relief Treatment - Low-temperature heat treatment for 3 hour at a temperature of 205°C is recommended for all hardened high- carbon steel parts. This should be done before the parts are mechanically pretreated, or enter the final pretreatment cycle, or both.

2.1.3 Mechanical Treatment - The purpose of mechanical treatment is to reduce subsequent acid pickling to a minimum. Where mechanical treatment has been accomplished with precision, it is sometimes possible to eliminate acid pickling entirely, thus improving the control of hydrogen embrittlement. When required, mechanical treatment of small parts is best effected by tumbling. All scaled and nearly all oil-quenched materials require mechanical cleaning such as by tumbling with or without abrasive, or by sand, grit, or vapour blasting. These operations should be carried out so as to avoid severe roughening of the surface with accompanying notch effect. Grinding is resorted to in certain cases where the surface smoothness or dimensions of the parts are of critical importance, for example, in chromium plating for engineering use.

3. FINAL PRETREATMENT PROCEDURES

3.1 Electrolytic Anodic Cleaning --All work, except work to be barrel plated, should preferably be cleaned in an electrolytic anodic alkaline cleaner. Anodic cleaning is recommended to avoid hydrogen embrittlement that is likely to result from cathodic cleaning. An exception is barrel work which, because of the work size, is preferably cleaned by soaking or tumbling in an alkaline cleaning solution without the use of current.

3.2 The purpose of this cleaning step is to remove completely the last traces of contaminants. In all cases it should be preceded by heavy- duty precleaning as covered in 2.1.1.

4

IS : 1985 ( Part I ) - 1980

3.3 The electrolytic anodic cleaner should be used at a temperature of 90°C or higher, and at- a current density of 500 A/m” or higher, in order that the required degree of cleanliness be obtained within a time period not exceeding two minutes.

3.4 On removal from the cleaner, the work should be thoroughly rinsed, first with water warmed to 50% and then in a cold-water spray at room temperature, prior to the acid dip.

3.5 Rinsing

3.5.1 The most thorough fresh-water rinsing operation possible is mandatory after each processing step if the best results in plating high- carbon steel are to be obtained. The purpose of rinsing is to eliminate drag-over by complete removal of the preceding solution from the surface of the work. Many existing commercial operations are characterized by inadequate rinsing.

3.5.2 Warm to hot rinses should be used following alkaline solution or where the subsequent processing solution is hot. The rinse temperature should not be so high as to induce drying of the steel surface between processing steps. Room temperature rinses are suitable for use following acid solutions where the solution in the next processing step is cold. In no case should very cold water be used for rinsing.

3.5.3 The recommended rinsing practice includes the use of an immersion rinse, followed always by a spray rinse of fresh water at the required temperature. The nonuse of spray rinsing is an invitation to trouble in the plating of high-carbon steel.

4. HYDROCHLORIC ACID TREATMENT

4.1 The purpose of the HCl treatment is to remove completely the last trace of oxide from the surface of the high-carbon steel. The intensity of HCl treatment should be held to the minimum required by the nature and amount of oxide present. The use of H&O4 instead of HCl is not recommended for descaling high-carbon steel because of its smut-forming tendency, inspite of the somewhat lowered tendency to rusting of HzSOI - treated surfaces. The addition of wetting agents to the HCI solution js not recommended. Care and caution shall be exercised in the use of inhibitors where they are required, since they sometimes interfere with adhesion. Inhibitors are of benefit only in special cases where surface finish and dimensions are of prime importance.

5. SMUT REMOVAL

5.1 When the HCl treatment of the high-carbon steel results in the presence of smut, the smut shall be removed before the surface is

5

IS : 1985 ( Part I ) - 1980

electroplated. Light oxides formed on exposure to air after acid treatment shall likewise be removed. This can be done by an anodic cyanide or alkaline treatment.

6. ANODIC, ACID ETCHING

6.1 The use of an anodic acid etch and subsequent rinse as final steps in the preparation for plating of high-carbon steel is of importance in securing adhesion. Without such an anodic treatment, poor adhesion may occur. The anodic acid treatment is capable of removing a small amount of smut formed by the preceding HCl treatment; more substantial amounts of smut should be removed according to the procedures described in 5.1.

6.2 A 250 to 1 000 g/ 1 HaSOd solution used at a temperature of not more than 30°C and preferably below 25°C is effective for anodic etching of high-carbon steel. The addition of 125 g/l of Na&04 (based on the anhydrous salt ) is of benefit for many steel grades. Anodic treatment in this solution for a time usually not exceeding one minute at a current density of 1 500 A/m2 ( range of 1 000 to 4 000 A/m” ) is sufficient. A high acid content, high current density, and low temperature ( with reference to the ranges specified ) will minimize the attack on the base metal and produce a smoother surface. This solution is very stable and not affected appreciably by iron build up. Besides securing adhesion of the subsequent electroplate, it improves the uniformity of the plate and reduces hydrogen embrittlement.

NOTE - In case visible smut is formed on the surface, a suitable smut-removing sequence may be used.

7. ELECTROPOLISHING

7.1 Electropolishing is used to remove highly stressed metal and metal debris from the surface of cold-worked steel, thereby improving the bond strength and corrosion resistance of electroplated coatings. It accomplishes this function without the tendency to form smut, which may result. from anodic etching. Since it does not etch the steel, it is preferred by some electroplaters to anodic etching for preparing steel surfaces for decorative plating.

7.2 An activating treatment after electropolishing may be beneficial to subsequent plating. An example of a suitable activating treatment is anodic cleaning followed by acid dipping. Electropolishing can be used in addition to or instead of anodic etching.

7.3 Electropolishing of fine-grained steel provides a uniform, smooth finish. Electropolishing of a coarse-grained structure results in lesser smoothness. In either case, however, a word of caution is interjected

IS : 1985 ( Part I ) - 1980

that any seams, voids, stringers, and other surface defects may be damaging to the appearance of the electroplated coating. Yet, the removal of sharp edges or scratches and the removal of nonmetallic inclusions in seams and stringers may reduce the harmful effect of these defects on the corrosion resistance of the electroplated steel.

8. NATURE OF STEEL

8.1 Hardness - High hardness is a major cause of cracking of the steel during or after plating. The recommended maximum hardness range for classes of products depends on their geometry and service requirements. Parts hardened by heat treatment should be inspected before plating for the presence of cracks by a suitable method such as magnetic or fluorescent powder inspection. \

9. ELECTROPLATING PROCEDURES

9.1 Standard plating procedures may be used on high-carbon steel when the proper preparatory steps described in 2 and 3 have been selected and followed. The conditions of use of the plating bath should assure a minimum evolution of hydrogen at the cathode surface ( highest cathode current efficiency ). The use of the minimum length of time in each step of preparation and plating is recommended. The material should be handled with the minimum number of steps consistent with proper treatment.

9.2 The electrodeposition of tin and cadmium on high-carbon steel is easier to accomplish than that of zinc. Electrodeposition of nickel and chromium is not difficult if the recommended practice is followed. .Low internal stress of the deposit is desirable.

9.3 Springs and similar materials should not be plated while subject to externally applied stress.

10. HEAT TREATMENT AFTER ELECTROPLATING

10.1 Application - One purpose of the special preparatory treatments of high-carbon steel (2 and 3 ) is to minimize hydrogen embrittlement. In most commercial production it is necessary to take the electroplated work for final embrittlement relief. With springs and similar material, precautions should be observed to avoid flexing the articles before they are baked.

10.2 Procedure -The hydrogen may be largely removed and the physical properties of the steel substantially restored by heating for example, for 1 to 5 h in an oven maintained at a temperature of 150 to

7

IS : 1985 ( Part I ) - 1980

26O”C, the temperature and length of treatment depending on the severity of embrittlement, the cross section of the article, the requirements of the steel, and the kind and thickness of the electrodeposited coatings. The baking should be done as soon as possible after electroplating, and before any supplementary chemical treatment of the plated surfaces. The best time and temperature in some cases shall be established by experiment. A temperature not exceeding 205% is recommended for zinc- or cadmium-plated articles. A lower temperature may be required if the coating is to be given a subsequent chemical treatment.

8