This part of JB/T 8118 specifies the technical requirements, inspection and evaluation methods, and grades of metallographic structure of carburized layer depth and metallographic structure of piston pins of internal combustion engines made of 20, 15Cr, 20Cr or 20Mn2 steel after heat treatment.
This part is applicable to the inspection for carburized layer depth and metallographic structure of piston pin of reciprocating internal combustion engine with cylinder diameter less than 200mm.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of JB/T 8118. For dated reference, subsequent amendments to (excluding any corrigendum), or revisions of, any of these publications do not apply. However, parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. For undated references, the latest editions apply to this part.
3.1.1 The carburized layer depth is the hypereutectoid layer plus 1/2 transition layer of the eutectoid layer.
3.1.2 The carburized layer depth shall be in accordance with JB/T 8118-1997, 4.3.2.
3.1.3 For the outer surface with the carburized layer depth not greater than 0.6mm, the sum of the hypereutectoid layer plus the eutectoid layer shall account for 25% to 70% of the carburized layer depth, and no eutectoid layer is allowed.
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3.2 Hardened layer depth
3.2.1 The hardened layer depth is the vertical distance from the outer surface of piston pin to the specified inside hardness value position. For quality carbon structure steel, the limit hardness value is 550HV0.2; for alloy structure steel, the limit hardness value is 500HV0.2.
3.2.2 The hardened layer depth shall be in accordance with JB/T 8118-1997 (2009), 4.3.3.
JB/T 8118.2-2011 The following standards are cited：
