GMW GMW17346 PDF

Note: Nothing in this standard supercedes applicable laws and regulations.

Note: In the event of conflict between the English and domestic language, the English language shall take precedence.

This standard covers the requirements for laser and induction hardening and tempering of the cylinder bores of gray iron cylinder blocks. This standard only covers the metallurgical (microstructure, case depth and hardness) requirements of the cylinder block and the methods to verify with subsequent images of the pill microstructure for reference in Appendix A.

Purpose/Material Description.

Cylinder bore hardening and tempering are heat treatment operations and shall be compliant to AIAG CQI-9 requirements. GM Customer Specifics, IATF 16949 requires all suppliers globally to be in compliance with AIAG CQI-9 Heat Treat document. Applicability and effectiveness of heattreating processes shall be determined utilizing AIAG CQI-9 Special Process: Heat Treat System Assessment (HTSA), published by AIAG, and records maintained. Deviations to the AIAG CQI-9 Special Process: Heat Treat System Assessment require GM material engineering approval and must be documented.

Hardening and tempering of the cylinder bores is performed to improve the wear-resistance in the upper piston ring reversal zone with either an induction or laser process, see Figure 1. The choice of induction or laser hardening and tempering for this task was due to flexibility in heating only the precise area required and short cycle time. Additionally, the martensitic transformation results in an increase in specific volume, thus the pill pattern was developed to minimize the impact on cylinder bore distortion. Induction and laser heat treatments of ferrous materials entails four basic steps; heating to the austenitizing temperature; holding to fully convert the structure to austenite; and rapidly cooling to convert the austenite to martensite. In addition, hardened pills on the cylinder bores are subsequently tempered to improve material toughness and wear resistance.

Symbols.

Not applicable.

Applicability.

Hardening and tempering of the cylinder bore inner diameter of cast iron blocks. This specification is limited to assessing the hardening and tempering process in producing the honed transformed microstructure, total case depth and hardness within the pills. This standard does not apply to heat treatment of cylinder bore liners.

Remarks.

Appendix A contains microstructure images within the pill zones for reference.