ASTM B850-98 pdf download.Standard Guide for Post-Coating Treatments of Steel for Reducing the Risk of Hydrogen Embrittlement.
4. Requirements
4.1 Heat treatment may be performed on coated metals to reduce the risk of hydrogen embrittlement. The duration of heat treatment in all cases shall commence from the time at which the whole of each part attains the specified temperature.
4.2 Parts made from steel with actual tensile strengths ≥1000 MPa (with corresponding hardness values of 300 HV 10kgf , 303 HB, or 31 HR C ) and surface-hardened parts may require heat treatment unless Class ER-0 is specified. Prepara- tion involving cathodic treatments in alkaline or acid solutions shall be avoided. Additionally, the selection of electroplating solutions with high cathodic efficiencies is recommended for steel components with tensile strengths above 1400 MPa (with corresponding hardness values of 425 HV 10kgf , 401 HB, or 43 HR C ).
4.3 Table 1 provides a list of embrittlement-relief heat- treatment classes from which the purchaser may specify the treatment required to the electroplater, supplier, or processor on the part drawing or purchase order. N OTE 2—The treatment class selected is based on experience with the part, or similar parts, and the specific alloy used or with empirical test data. Because of factors such as alloy composition and structure, type of coating, coating thickness, size, mass, or design parameters, some parts may perform satisfactorily with no embrittlement-relief treatment. Class ER-0 treatment is therefore provided for parts that the purchaser wishes to exempt from treatment.
N OTE 3—The use of inhibitors in acid pickling baths may not minimize hydrogen embrittlement. 4.4 The electroplater, supplier, or processor is not normally in possession of the necessary information, such as design considerations, operating stresses, etc., that must be considered when selecting the correct embrittlement relief treatment. It is in the purchaser’s interest that his or her part designer, manufacturing engineer, or other technically qualified indi- vidual specify the treatment class on the part drawing or purchase order.
5. Embrittlement Relief Treatment Classes
5.1 With the exception of surface-hardened parts and parts that have been shot peened in accordance with Specification B851, heat treatment conditions may be selected on the basis of actual tensile strength. When only the minimum tensile strength is specified, or if the tensile strength is not known, the heat treatment condition may be selected by relating known or measured hardness values to equivalent tensile strengths. It is recommended that the tensile strength be supplied by the purchaser. 5.2 Steels that have been wholly or partly surface hardened may be considered as being in the category appropriate to the hardness of the surface-hardened layer.
5.3 If the purchaser requires any tests to be performed in order to verify adequate embrittlement relief treatment, the test method and the sampling plan to be used shall be specified.
6. Heat Treatment After Processing
6.1 The heat treatment shall commence as soon as possible, preferably within 1 h but not later than 3 h after plating and before commencement of any grinding or other mechanical operation. For cadmium, tin, zinc, their alloys, or any other coating receiving a chromate treatment, heat treatment shall be conducted before chromate treatment. N OTE 4—Chromate coatings undergo change at temperatures above 66°C. The coating changes from an amorphous structure to a crystalline structure and no longer exhibits self-healing properties. While the crys- tallized chromate coating will provide satisfactory corrosion protection under most natural environments, the chromate coating will no longer pass accelerated corrosion tests. N OTE 5—The time period referred to is the length of time between the end of the plating operation and loading of the item concerned into the heat treatment processor.
.2 For high-strength steels, the conditions given in Table 1 may be applied. For steels ofactual tensile strength below 1000 MPa, heat treatment after plating is not essential.
6.3 Electroplated steel items having surface-hardened areas and through hardened or bearing steels, which would suffer an unacceptable reduction in hardness by treatment in accordance with Table 1 shall be heat treated at a lower temperature, but not below 130°C. 6.4 Treatment at 440 to 480°C will reduce the hardness of chromium deposits. It shall not be applied to steels that may be affected adversely by heat treatment at this temperature, and the lower temperature range shall be applied. For tempered steels, items shall not be heat treated above a temperature that shall be 50°C below the tempering temperature.ASTM B850 pdf download.