# Tempering Hollomon-Jaffe Parameter Calculator

> Source: https://netray.co/tools/tempering-hollomon-jaffe-parameter-calculator
> Publisher: Netray (netray.co), AI and integration engineering for ERP and manufacturing systems.
> Section: Free Tools

## Short answer

Compute the Hollomon-Jaffe tempering parameter and the equivalent time at another temperature, or the temperature that gives the same softening in a target time.

## Category

manufacturing

## Industry

Foundry and Forging

## Audience

- Heat treat engineer
- Metallurgist
- Quality engineer

## Tool

**Kind:** calculator

**Inputs:**

#### Reference tempering temperature

**Key:** temper_t1

**Type:** number

**Default:** 600

**Min:** 100

**Max:** 750

**Step:** 5

**Unit:** deg C

#### Reference time at temperature

**Key:** hours_1

**Type:** number

**Default:** 2

**Min:** 0.05

**Step:** 0.25

**Unit:** hours

#### Alternative temperature

**Key:** temper_t2

**Type:** number

**Default:** 560

**Min:** 100

**Max:** 750

**Step:** 5

**Unit:** deg C

#### Target time for temperature solve

**Key:** target_hours

**Type:** number

**Default:** 1

**Min:** 0.05

**Step:** 0.25

**Unit:** hours

**Help:** Used to find the temperature that gives the same parameter in this time.

#### Material constant C

**Key:** c_const

**Type:** number

**Default:** 20

**Min:** 10

**Max:** 30

**Step:** 0.5

**Help:** About 20 for many carbon and low alloy steels with time in hours. Use your alloy's published value when known.

**Outputs:**

#### Hollomon-Jaffe parameter P

**Key:** p_hj

**Expr:** (temper_t1 + 273.15) * (c_const + log10(hours_1))

**Format:** integer

**Description:** P = T(K) x (C + log10 t), t in hours.

#### Equivalent time at alternative temperature

**Key:** hours_2

**Expr:** pow(10, p_hj / (temper_t2 + 273.15) - c_const)

**Format:** hours

**Primary:** true

#### Equivalent temperature for target time

**Key:** temp_eq

**Expr:** p_hj / (c_const + log10(target_hours)) - 273.15

**Format:** decimal

**Primary:** true

**Description:** In deg C.

**Chart:**

#### Equivalent temperature vs tempering time

**Type:** line

**X:** target_hours

**From:** 0.25

**To:** 8

**Steps:** 30

**Series:**

- temp_eq

**Disclaimer:** Equivalence is an empirical aid for similar steels and tempering ranges. Always confirm hardness on a test coupon, and follow your controlled specification for the production cycle.

## Content

**Intro:** The Hollomon-Jaffe parameter lets a metallurgist trade time against temperature when tempering steel. If a furnace is down or a load must be finished quickly, this tool estimates an equivalent cycle that produces similar softening.

**Sections:**

#### How to use the calculator

**Body:** Enter the proven tempering temperature and time, then either a different temperature to learn the new time, or a target time to learn the temperature. The parameter P stays the same, so any pair with the same P should give approximately the same hardness for a given steel.

**Bullets:**

- Use hours for time and degrees Celsius for temperature.
- Keep the alternative temperature within the same tempering range.
- Confirm with a hardness test on a sample.

#### The method behind it

**Body:** The parameter is P = T x (C + log10 t), with T in kelvin and t in hours. C is a material constant, around 20 for many steels. Because tempering is diffusion controlled, a small drop in temperature requires a much longer time for the same result: the relationship is logarithmic in time and linear in temperature. The tool solves for t at a second temperature, or for T at a chosen time.

#### Reading the result and common mistakes

**Body:** For the default 600 deg C for 2 hours, tempering at 560 deg C needs roughly 19 hours, which shows how steep the trade is. Moving up in temperature shortens time but increases the risk of overshoot and temper embrittlement in susceptible steels. Do not use the equivalence across ranges that cross a secondary hardening or embrittlement zone.

**Bullets:**

- Applying the result to steels with strong secondary hardening.
- Entering minutes instead of hours.
- Ignoring furnace load heat-up time in the true time at temperature.
- Skipping the hardness check after a changed cycle.

**Cta:** If heat treat cycles and certifications are stored in your ERP or QMS, we can discuss how to make them searchable for the shop. The calculator is free either way.

**Faq:**

#### What is the Hollomon-Jaffe parameter?

**Answer:** It is a time-temperature parameter, P = T x (C + log10 t), used to compare tempering cycles. Two cycles with the same P produce about the same hardness in a given steel. It is similar in form to the Larson-Miller parameter used for creep.

#### What value of C should I use?

**Answer:** A value near 20 with time in hours is common for many carbon and low alloy steels. Alloy steels may differ, and published curves for your grade are better. If you have two hardness-matched cycles, you can back out C.

#### Is the time the total cycle time?

**Answer:** No, it is time at temperature, measured once the load core has reached the setpoint. Heat-up time in a dense load can be significant, so confirm the thermocouple placement and soak definition in your procedure.

#### Can I change a customer-approved cycle with this?

**Answer:** Only if the customer specification and your process approval allow it. Treat the tool as an engineering estimate, then qualify the new cycle with hardness and mechanical testing and record the change through your normal controls.

## Search terms

hollomon jaffe parameter calculator, tempering time temperature equivalence, larson miller tempering, tempering parameter steel, equivalent tempering cycle, heat treatment tempering calculator, tempering time vs temperature, time temperature tempering trade off

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