Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
(OP)
Need information w.r.t annealing of 0.06% C steel rivets. Annealing at 1700F for 1hr is producing fully annealed structure with grain size number between 6 and 7.
Hardness measurement using vickers microhardness is not consistent. Need the hardness strictly max 60HRB.
Same rivet giving different hardness(73HRB and 56HRB).
Annealing time changed from 1hr to 1.5hr soaking time but no help. Please guide me through. Should I increase the annealing time at 1700F?
Hardness measurement using vickers microhardness is not consistent. Need the hardness strictly max 60HRB.
Same rivet giving different hardness(73HRB and 56HRB).
Annealing time changed from 1hr to 1.5hr soaking time but no help. Please guide me through. Should I increase the annealing time at 1700F?





RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
rivets are 0.020"dia with 0.060" long. 1010 steel rivets heat treated at 1700F for 1,1.5hr and 5hrs soak time.
Measurement on 5 rivets after 5hours of soak time gave 3 results less than 60HRB and 2 were 67 and 69HRB out of spec.
300gmf and 100gmfloads gave higher microhardness data probably due to indentation size effects.
Chemistry of raw material is within spec. Tensile strength of wire(raw material) was reported higher than required but since we have annealed it for so long, that effect of higher tensile strength must be lost by now.
Thanks guys for all your input.
TVP: around 9000 pieces roughly are annealed at a time in a vacuum furnace and slow cooling is carried out in vaccum.
Rivets are spread out on a tray before heat treating.
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
2. Is the indentation size measured automatically or by hand? Indentation measuring software can be thrown off by all kinds of things, it is always good to double-check by an operator. And in a borderline case like you describe, I would consider it a good idea for a second person, even, to check that the measuring lines are correctly placed at the corners of the indentation.
3. Presumably you have a calibrated test block that you verify regularly? When you look over the records of your verifications with the calibrated test block, is there any tendency to readings on the high or low side of the calibrated range? This may reveal a bias on how indentations are measured (whether by software or operator).
4. What magnification is being used? Lower magnifications result in less accurate measurements.
5. Can your machine test at 1000g load? That might give you more consistent results.
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
Indentation for hard ones showed more sinking in type of behavior around the indent whereas for indents within spec, indent looked normal.
We do not have test block for low hardness ranges i.e 100HV for 500gmf.The lowest we have is 241HV.
Indentation area is measured automatically. But we tried doing it manually as well and gave around similar result.
Our machine can measure at 1000gmf load but the rivets are o.02"dia with 0.06"long. So indent might crossover and give erroneous reading.
Will the test block in low hardness ranges between 90-110HV using 500gmf load be helpful in reducing the hardness inconsistancy within the same rivet.
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
If I read correctly, you're extrapolating HRB from Vickers indents?
The rivets are small at 0.5mm dia x 1.5mm long.
Pure guess on my part, but it sounds material related (two batches?, especially if the initial hardness was high for some and grain boundaries appear to be pinned)
or hardness testing setup
If you're at a wit's end, maybe even try an anneal for 0.5hr - you may be getting segregation. After all, at a 0.5mm dia rivet, soak time needed is minimal. I'm not aware of minimum recommended soak times from standard or manufacture, so this may not be possible.
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax
How many indentations are you able to fit on each rivet? Two indentations too close together can make the second one artificially hard due to work hardening; the ASTM rule is to have empty space with a minimum width of two indentations between each mark.
Is it possible the parts are being work hardened by any deformation that is part of the sample prep? Grinding and polishing should be OK, but (for example) using wire cutters to make an appropriate shaped sample for mounting might introduce some work hardening.
Another thing to look at might be material. Do you have chemical analysis of the material lot? If there are any high residual elements, there might be banding (alloy segregation). Bands with higher levels of alloying elements would have higher hardness.
RE: Need input w.r.t annealing of low carbon steel rivet where hardness after heat treat be 60hrbmax